The present invention relates to sintered metal oxides of great use as blanks for transparent electroconductive films for display devices and others, to targets of the sintered products for forming transparent electroconductive films, to transparent electroconductive materials, and to transparent electroconductive glass and films formed from the targets.
Recently, various display devices such as liquid-crystal displays, electroluminescent displays, field emission displays and others have been introduced into office appliances and also control systems in factories. These devices all have a sandwich structure with a display member put between transparent electroconductive films.
For the transparent electroconductive films, much used is indium oxide-tin oxide (hereinafter referred to as ITO) to give ITO films. The ITO films are highly transparent and have low electric resistance, and, in addition, they are well etched and their adhesiveness to substrates is good. As having such good properties, the ITO films are widely used in the art. In general, the ITO films are formed in various methods of sputtering, ion-plating, vapor deposition, etc.
Though having such good properties, however, there still remain some problems to be solved with the ITO films when they are used, for example, as transparent electrodes for liquid-crystal display devices. The problems with the ITO films include their surface accuracy, the tapering processability of electrodes made of them, and their workability into electrodes with junctions or contact points.
Specifically, ITO itself is a crystalline metal oxide, and its crystal grains grow in the step of forming it into films. The growing crystal grains deposit on the surface of the ITO film, thereby lowering the surface accuracy of the film. In the step of etching the ITO film for forming an electrode, the intergranular boundaries in the film are first etched, and the etched surface of the electrode shall be roughened. Therefore, it is difficult to etch the ITO film with accuracy. Further, in the step of tapering the ITO film electrode, the intergranular boundaries in the film are also first etched, and the ITO grains will often remain in the etched area. In that condition, the ITO film electrode could not be well insulated from the counter electrode, thereby often causing display failure.
To solve the problem, a transparent electroconductive material comprising indium oxide and zinc oxide was proposed, for example, in Japanese Patent Laid-Open No. 234565/1994. Its workability into electrodes was improved without its transparency and electroconductivity being not sacrificed. However, the indium oxide-zinc oxide material has a bulk resistance of from 2 to 5 mxcexa9.cm, and the electric power to be applied thereto for forming it into films is limited. Therefore, the problem with the material is that the productivity in forming it into films is low.
In an organic electroluminescent device having a film electrode of ITO, holes must be transferred from the ITO film electrode into the light emission layer or into the hole transporting layer. For this, it is desirable that the work function of the electrode material and that of the organic compound for the light emission layer or the hole transporting layer are nearly on the same level and that the energy gap between the anode and the hole transporting layer is as small as possible. To reduce the energy gap, the difference between the work function of the anode material and the ionization potential of the organic compound for the hole transporting layer must be reduced. Various organic compounds have been proposed for hole-transporting substances usable for forming the hole transporting layer. Of those, aromatic amine compounds, especially triphenylamine derivatives have been known to have good capabilities. Triphenylamine, one of triphenylamine derivatives, has an ionization potential of from 5.5 to 5.6 electron volts. On the other hand, for transparent electroconductive films, well known is indium oxide-tin oxide (hereinafter referred to as ITO) having high transparency and low electric resistance. The work function of ITO is 4.6 electron volts. Accordingly, there shall be a relatively large energy gap between the anode and the electron transportation layer both of such ordinary materials.
In that situation, proposed was an organic, light-emitting thin-film device having an organic compound layer between an anode and a cathode, for example, in Japanese Patent Laid-Open No. 63771/1997. In this, the anode is of a thin film of a metal oxide of which the work function is larger than that of ITO. However, the thin-film anode of such a metal oxide has a light transmittance of 10% when the metal oxide is ruthenium oxide, and 20% when it is vanadium oxide. To increase the light transmittance, proposed was a two-layered structure composed of an ITO film and an ultra-thin film of the metal oxide, the ultra-thin film having a thickness of not larger than 300 angstroms. Even in this case, however, the light transmittance of the two-layered structure is still 40 to 60% or so. Therefore, the two-layered structure is still problematic in that its transparency is not satisfactory for transparent electrodes for display devices.
The present invention is to provide sintered metal oxides capable of being formed into films in a stable and efficient manner through sputtering or the like, targets of the sintered products, and transparent electroconductive glass and films formed from the targets. The transparent electroconductive glass and films have good transparency, good electroconductivity and good workability into electrodes, and when they are formed into transparent electrodes and used in organic electroluminescent devices, the difference between their work function and the ionization potential of the hole-transporting substances in the devices is small and therefore the transparent electrodes do not lower the light emission efficiency of the devices.
Having assiduously studied so as to solve the problems noted above, we, the present inventors have found that using sintered products of compounds, which comprise indium oxide, tin oxide and zinc oxide in a specific ratio, as transparent electroconductive materials solves the problems. On the basis of this finding, we have completed the present invention.
Specifically, the invention includes first to fourth aspects, which are summarized as follows:
[I] First Aspect of the Invention
[1] A sintered product that comprises constituent components of indium oxide, tin oxide and zinc oxide in the following atomic ratios:
In/(In+Sn+Zn)=0.50 to 0.75,
Sn/(In+Sn+Zn)=0.20 to 0.45,
Zn/(In+Sn+Zn)=0.03 to 0.30,
and contains a hexagonal layer compound of In2O3.(ZnO)m with m indicating an integer of from 2 to 20, and a spinel-structured compound of Zn2SnO4.
[2] The sintered product of above [1], which has a specific resistance of smaller than 2 mxcexa9.cm.
[3] A sintered product that comprises constituent components of indium oxide, tin oxide and zinc oxide in the following atomic ratios:
In/(In+Sn+Zn)=0.50 to 0.75,
Sn/(In+Sn+Zn)=0.20 to 0.45,
Zn/(In+Sn+Zn)=0.03 to 0.30,
and from 0.5 to 10 atomic %, relative to the total of all metal atoms therein, of an oxide of a positive tetra-valent or higher poly-valent metal, and contains a hexagonal layer compound of In2O3.(ZnO)m with m indicating an integer of from 2 to 20, and a spinel-structured compound of Zn2SnO4.
[4] The sintered product of above [3], in which the oxide of a positive tetra-valent or higher poly-valent metal is ruthenium oxide, molybdenum oxide or vanadium oxide.
[5] A sputtering target for transparent electroconductive films, which comprises the sintered product of any of above [1] to [4].
[6] An electron-beaming target for transparent electroconductive films, which comprises the sintered product of any of above [1] to [4].
[7] An ion-plating target for transparent electroconductive films, which comprises the sintered product of any of above [1] to [4].
[8] Transparent electroconductive glass prepared by coating the surface of glass with an amorphous transparent electroconductive film that comprises constituent components of indium oxide, tin oxide and zinc oxide in the following atomic ratios:
In/(In+Sn+Zn)=0.50 to 0.75,
Sn/(In+Sn+Zn)=0.20 to 0.45,
Zn/(In+Sn+Zn)=0.03 to 0.30,
and contains from 0.5 to 10 atomic %, relative to the total of all metal atoms therein, of an oxide of a positive tetra-valent or higher poly-valent metal.
[9] The transparent electroconductive glass of above [8], in which the oxide of a positive tetra-valent or higher poly-valent metal is ruthenium oxide, molybdenum oxide or vanadium oxide.
[10] The transparent electroconductive glass of above [8] or [9], which has a light transmittance of at least 75% and a specific resistance of at most 5 mxcexa9.cm, and in which the transparent electroconductive film has a work function of at least 5.45.
[11] A transparent electroconductive film prepared by coating the surface of a transparent resin film with an amorphous transparent electroconductive layer that comprises constituent components of indium oxide, tin oxide and zinc oxide in the following atomic ratios:
In/(In+Sn+Zn)=0.50 to 0.75,
Sn/(In+Sn+Zn)=0.20 to 0.45,
Zn/(In+Sn+Zn)=0.03 to 0.30,
and contains from 0.5 to 10 atomic %, relative to the total of all metal atoms therein, of an oxide of a positive tetra-valent or higher poly-valent metal.
[12] The transparent electroconductive film of above [11], in which the oxide of a positive tetra-valent or higher poly-valent metal is ruthenium oxide, molybdenum oxide or vanadium oxide.
[13] The transparent electroconductive film of above [11] or [12], which has a light transmittance of at least 75% and a specific resistance of at most 5 mxcexa9.cm, and in which the transparent electroconductive layer has a work function of at least 5.45.
[II] Second Aspect of the Invention
[1] A sintered product of a composition that comprises indium oxide, or indium oxide and zinc oxide and/or tin oxide in the following atomic ratios:
In/(In+Zn+Sn)=0.80 to 1.00,
Zn/(In+Zn+Sn)=0.00 to 0.20,
Sn/(In+Zn+Sn)=0.00 to 0.20,
and contains from 0.5 to 10 atomic %, relative to the total of all metal atoms therein, of a metal oxide selected from ruthenium oxide, molybdenum oxide and vanadium oxide.
[2] A sintered product of a composition that comprises indium oxide and zinc oxide, or tin oxide in addition to the former two oxides in the following atomic ratios:
In/(In+Zn+Sn)=0.80 to 1.00,
Zn/(In+Zn+Sn)=0.05 to 0.20,
Sn/(In+Zn+Sn)=0.00 to 0.20,
and contains from 0.5 to 10 atomic %, relative to the total of all metal atoms therein, of a metal oxide selected from ruthenium oxide, molybdenum oxide and vanadium oxide.
[3] A sintered product of a composition that comprises indium oxide, zinc oxide and tin oxide in the following atomic ratios:
In/(In+Zn+Sn)=0.80 to 1.00,
Zn/(In+Zn+Sn)=0.05 to 0.20,
Sn/(In+Zn+Sn)=0.02 to 0.20,
and contains from 0.5 to 10 atomic %, relative to the total of all metal atoms therein, of a metal oxide selected from ruthenium oxide, molybdenum oxide and vanadium oxide.
[4] A sputtering target comprising the sintered product of any of above [1] to [3].
[5] An electron-beaming target comprising the sintered product of any of above [1] to [3].
[6] An ion-plating target comprising the sintered product of any of above [1] to [3].
[7] Transparent electroconductive glass prepared by coating the surface of glass with a transparent electroconductive film of a composition that comprises indium oxide, zinc oxide and tin oxide in the following atomic ratios:
In/(In+Zn+Sn)=0.80 to 1.00,
Zn/(In+Zn+Sn)=0.00 to 0.20,
Sn/(In+Zn+Sn)=0.00 to 0.20,
and contains from 0.5 to 10 atomic %, relative to the total of all metal atoms therein, of a metal oxide selected from ruthenium oxide, molybdenum oxide and vanadium oxide.
[8] The transparent electroconductive glass of above [7], which has a light transmittance of at least 75% and a specific resistance of at most 5 mxcexa9.cm, and in which the transparent electroconductive film has a work function of at least 5.45 electron volts.
[9] A transparent electroconductive film prepared by coating the surface of a transparent resin film with a transparent electroconductive layer that comprises indium oxide, zinc oxide and tin oxide in the following atomic ratios:
In/(In+Zn+Sn)=0.80 to 1.00,
Zn/(In+Zn+Sn)=0.00 to 0.20,
Sn/(In+Zn+Sn)=0.00 to 0.20,
and contains from 0.5 to 10 atomic %, relative to the total of all metal atoms therein, of a metal oxide selected from ruthenium oxide, molybdenum oxide and vanadium oxide.
[10] The transparent electroconductive film of above [9], which has a light transmittance of at least 75% and a specific resistance of at most 5 mxcexa9.cm, and in which the transparent electroconductive layer has a work function of at least 5.45 electron volts.
[III] Third Aspect of the Invention
[1] A transparent electroconductive material of a composition that comprises one or more metal oxides selected from indium oxide, zinc oxide and tin oxide and contains from 0.5 to 20 atomic %, relative to the total of all metal atoms therein, of one or more metal oxides selected from iridium oxide, rhenium oxide and palladium oxide.
[2] A transparent electroconductive material of a composition that comprises metal oxide(s) of indium oxide, zinc oxide and tin oxide in the following atomic ratios:
In/(In+Zn+Sn)=0.00 to 1.00,
Zn/(In+Zn+Sn)=0.00 to 0.25,
Sn/(In+Zn+Sn)=0.00 to 1.00,
and contains from 0.5 to 20 atomic %, relative to the total of all metal atoms therein, of one or more metal oxides selected from iridium oxide, rhenium oxide and palladium oxide.
[3] A transparent electroconductive material of a composition that comprises metal oxides of indium oxide, zinc oxide and tin oxide in the following atomic ratios:
In/(In+Zn+Sn)=0.50 to 1.00,
Zn/(In+Zn+Sn)=0.05 to 0.25,
Sn/(In+Zn+Sn)=0.00 to 0.50,
and contains from 0.5 to 20 atomic %, relative to the total of all metal atoms therein, of one or more metal oxides selected from iridium oxide, rhenium oxide and palladium oxide.
[4] A transparent electroconductive material of a composition that comprises metal oxides of indium oxide, zinc oxide and tin oxide in the following atomic ratios:
In/(In+Zn+Sn)=0.75 to 0.95,
Zn/(In+Zn+Sn)=0.05 to 0.20,
Sn/(In+Zn+Sn)=0.00 to 0.20,
and contains from 0.5 to 20 atomic %, relative to the total of all metal atoms therein, of one or more metal oxides selected from iridium oxide, rhenium oxide and palladium oxide.
[5] A sintered product prepared by sintering the composition of any of above [1] to [4].
[6] A sputtering target comprising the sintered product of above [5].
[7] Transparent electroconductive glass prepared by coating the surface of glass with a transparent electroconductive film of a composition that comprises one or more metal oxides selected from indium oxide, zinc oxide and tin oxide and contains from 0.5 to 20 atomic %, relative to the total of all metal atoms therein, of one or more metal oxides selected from iridium oxide, rhenium oxide and palladium oxide.
[8] The transparent electroconductive glass of above [7], which has a light transmittance of at least 70% and in which the transparent electroconductive film has a work function of at least 5.4 electron volts.
[9] A transparent electroconductive film prepared by coating the surface of a transparent resin film with a transparent electroconductive layer that comprises one or more metal oxides selected from indium oxide, zinc oxide and tin oxide and contains from 0.5 to 20 atomic %, relative to the total of all metal atoms therein, of one or more metal oxides selected from iridium oxide, rhenium oxide and palladium oxide.
[10] The transparent electroconductive film of above [9], which has a light transmittance of at least 70% and in which the transparent electroconductive layer has a work function of at least 5.4 electron volts.
Fourth Aspect of the Invention [1] A transparent electroconductive material of a composition that comprises metal oxide(s) of tin oxide, indium oxide and zinc oxide in the following atomic ratios:
Sn/(Sn+In+Zn)=0.55 to 1.00,
In/(Sn+In+Zn)=0.00 to 0.45,
Zn/(Sn+In+Zn)=0.00 to 0.25,
and contains from 0.5 to 10 atomic %, relative to the total of all metal atoms therein, of one or more metal oxides selected from vanadium oxide, molybdenum oxide and ruthenium oxide.
[2] The transparent electroconductive material of above [1], in which tin oxide, indium oxide and zinc oxide are in the following atomic ratios:
Sn/(Sn+In+Zn)=0.55 to 0.95,
In/(Sn+In+Zn)=0.00 to 0.40,
Zn/(Sn+In+Zn)=0.05 to 0.25.
[3] The transparent electroconductive material of above [1], in which tin oxide, indium oxide and zinc oxide are in the following atomic ratios:
Sn/(Sn+In+Zn)=0.55 to 0.95,
In/(Sn+In+Zn)=0.00 to 0.40,
Zn/(Sn+In+Zn)=0.05 to 0.20.
[4] The transparent electroconductive material of above [1], in which tin oxide, indium oxide and zinc oxide are in the following atomic ratios:
Sn/(Sn+In+Zn)=0.60 to 0.95,
In/(Sn+In+Zn)=0.00 to 0.35,
Zn/(Sn+In+Zn)=0.05 to 0.20.
[5] A sintered product prepared by sintering the composition of any of above [1] to [4] at a temperature of not lower than 1200xc2x0 C.
[6] A sputtering target comprising the sintered product of above [5], which has a specific resistance of at most 10 mxcexa9.cm.
[7] Transparent electroconductive glass prepared by forming, on the surface of a glass substrate, a transparent electroconductive film of a composition that comprises metal oxide(s) of tin oxide, indium oxide and zinc oxide in the following atomic ratios:
Sn/(Sn+In+Zn)=0.55 to 1.00,
In/(Sn+In+Zn)=0.00 to 0.45,
Zn/(Sn+In+Zn)=0.00 to 0.25,
and contains from 0.5 to 10 atomic %, relative to the total of all metal atoms therein, of one or more metal oxides selected from vanadium oxide, molybdenum oxide and ruthenium oxide.
[8] The transparent electroconductive glass of above [7], in which the transparent electroconductive film has a light transmittance of at least 70% and a work function of at least 5.4 electron volts.
[9] A transparent electroconductive film prepared by forming, on the surface of a transparent resin film, a transparent electroconductive layer of a composition that comprises metal oxide(s) of tin oxide, indium oxide and zinc oxide in the following atomic ratios:
Sn/(Sn+In+Zn)=0.55 to 1.00,
In/(Sn+In+Zn)=0.00 to 0.45,
Zn/(Sn+In+Zn)=0.00 to 0.25,
and contains from 0.5 to 10 atomic %, relative to the total of all metal atoms therein, of one or more metal oxides selected from vanadium oxide, molybdenum oxide and ruthenium oxide.
[10] The transparent electroconductive film of above [9], in which the transparent electroconductive layer has a light transmittance of at least 70% and a work function of at least 5.4 electron volts.
Embodiments of the invention are described below.
First Aspect of the Invention
The sintered product of the invention is a transparent electroconductive material for forming transparent electroconductive films, and its basic constituent components are indium oxide, tin oxide and zinc oxide.
In this, the constituent components are in the following atomic ratios:
In/(In+Sn+Zn)=0.50 to 0.75,
Sn/(In+Sn+Zn)=0.20 to 0.45,
Zn/(In+Sn+Zn)=0.03 to 0.30,
preferably,
xe2x80x83In/(In+Sn+Zn)=0.60 to 0.75,
Sn/(In+Sn+Zn)=0.20 to 0.35,
Zn/(In+Sn+Zn)=0.05 to 0.20,
more preferably,
In/(In+Sn+Zn)=0.60 to 0.70,
Sn/(In+Sn+Zn)=0.25 to 0.35,
Zn/(In+Sn+Zn)=0.05 to 0.15.
In the invention, the composition of the constituent components, indium oxide, tin oxide and zinc oxide is defined as above. This is because when a mixture of indium oxide and zinc oxide is baked at low temperatures, the electroconductivity of the resulting sintered product is low. In the invention, the reduction in the electroconductivity of the sintered product is prevented. When the mixture of indium oxide and zinc oxide is baked at high temperatures, the resulting sintered product could be a hexagonal layer compound with increased electroconductivity. In the mixture, however, it is difficult to convert zinc oxide entirely into a hexagonal layer compound, and the increase in the electroconductivity of the sintered product is limited. Accordingly, in the invention, zinc oxide that could not be converted into a hexagonal layer compound is reacted with tin oxide to form a spinel-structured compound, whereby the electroconductivity of the sintered product of the composition is increased and the sputtering stability of targets of the sintered product is ensured.
Regarding the blend ratio of these components, if the atomic ratio of indium oxide is smaller than 0.50, the surface resistance of the transparent electroconductive film to be obtained herein will be high and the heat resistance thereof will be low; but if larger than 0.75, the transparent electroconductive film will crystallize to lower its transparency. If the atomic ratio of tin oxide is smaller than 0.20, forming the spinel-structured compound of zinc oxide and tin oxide will be incomplete; but if larger than 0.45, the surface resistance of the transparent electroconductive film will be high. If the atomic ratio of zinc oxide is smaller than 0.03, the transparent electroconductive film will readily crystallize; but if larger than 0.30, the heat resistance of the film will be low.
The sintered product comprises the constituent metal oxides of which the composition falls within the defined range as above, and contains a hexagonal layer compound of In2O3.(ZnO)m with m indicating an integer of from 2 to 20, and a spinel-structured compound of Zn2SnO4.
The sintered product of the invention that comprises the constituent components as above has high electroconductivity as so mentioned hereinabove, and its specific resistance is lower than 2 mxcexa9.cm. Accordingly, when a target of the sintered product is sputtered to form a film in a sputtering device, the sputtering stability is good and the productivity in producing the film product is good.
The sintered product that comprises the constituent components, indium oxide, tin oxide and zinc oxide, and additionally contains from 0.5 to 10 atomic %, relative to the total of all metal atoms therein, an oxide of a positive tetra-valent or higher poly-valent metal, especially preferably ruthenium oxide, molybdenum oxide or vanadium oxide has a work function falling between 5.45 and 5.70 electron volts, and its work function is nearly on the same level as the average work function, 5.6 electron volts, of organic compounds for light-emitting substances or hole-transporting substances for organic electroluminescent devices. Accordingly, transparent electroconductive films formed by sputtering a target of the sintered product shall have high hole injection efficiency when used in organic electroluminescent devices. In the sintered product, the proportion of the oxide of a positive tetra-valent or higher poly-valent metal preferably falls between 1 and 5 atomic % to the total of all metal atoms.
For producing the sintered product of the invention, for example, employed is a method comprising uniformly mixing and grinding powders of starting metal oxides in a mixing and grinding machine, for example, in a wet ball or bead mill or ultrasonically, then granulating the resulting mixture, shaping the resulting granules into bodies of desired form by pressing, and finally baking them into sintered products. In this, the raw material powders are preferably mixed and ground as fine as possible, but, in general, they are mixed and ground to have a mean grain size of not larger than 1 xcexcm. In the baking step, the shaped bodies are baked generally at a temperature falling between 1,200 and 1,500xc2x0 C., but preferably between 1,250 and 1,480xc2x0 C., for a period of time generally falling between 10 and 72 hours, but preferably between 24 and 48 hours. In this, the heating rate may fall between 1 and 50xc2x0 C./min.
In the baking step, the baking temperature is preferably not lower than 1,250xc2x0 C. in order that indium oxide and zinc oxide in the resulting sintered product could form a hexagonal layer compound of the formula noted above. The baking temperature shall be at lowest 1,000xc2x0 C. in order that zinc oxide and tin oxide could form a spinel-structured compound.
Where the three-component system of the metal oxides is combined with an oxide of a positive tetra-valent or higher poly-valent metal, such as ruthenium oxide, molybdenum oxide or vanadium oxide in preparing the sintered product of the invention, a suitable amount of powder of the additional metal oxide such as ruthenium oxide is added to the powders of the starting, three-component system metal oxides, and baked in the same manner as above. Also in this case, baking the shaped bodies is effected under the condition under which the hexagonal layer compound of indium oxide and zinc oxide and the spinel-structured compound of zinc oxide and tin oxide could be formed in the resulting sintered product.
[II] Second Aspect of the Invention
The sintered product of the invention for forming transparent electroconductive films is of a composition that comprises indium oxide, or indium oxide and zinc oxide and/or tin oxide in the following atomic ratios:
In/(In+Zn+Sn)=0.80 to 1.00,
Zn/(In+Zn+Sn)=0.00 to 0.20,
Sn/(In+Zn+Sn)=0.00 to 0.20,
and contains from 0.5 to 10 atomic %, relative to the total of all metal atoms therein, of a metal oxide selected from ruthenium oxide, molybdenum oxide and vanadium oxide.
More preferably, the sintered product is of a composition that comprises indium oxide and zinc oxide, or tin oxide in addition to the former two oxides in the following atomic ratios:
In/(In+Zn+Sn)=0.80 to 1.00,
Zn/(In+Zn+Sn)=0.05 to 0.20,
Sn/(In+Zn+Sn)=0.00 to 0.20,
and contains from 0.5 to 10 atomic %, relative to the total of all metal atoms therein, of a metal oxide selected from ruthenium oxide, molybdenum oxide and vanadium oxide.
Most preferably, the sintered product is of a composition that comprises indium oxide, zinc oxide and tin oxide in the following atomic ratios:
In/(In+Zn+Sn)=0.80 to 1.00,
Zn/(In+Zn+Sn)=0.05 to 0.20,
Sn/(In+Zn+Sn)=0.02 to 0.20,
and contains from 0.5 to 10 atomic %, relative to the total of all metal atoms therein, of a metal oxide selected from ruthenium oxide, molybdenum oxide and vanadium oxide.
For the sintered product of the invention, the composition of the basic constituent components, indium oxide, tin oxide and zinc oxide, may be indium oxide alone, or a mixture of indium oxide and a small amount of zinc oxide, or a mixture of indium oxide, a small amount of zinc oxide and a small amount of tin oxide, as in the above.
Regarding the blend ratio of the constituent components, if the atomic ratio of indium oxide is smaller than 0.80, the surface resistance of the transparent electroconductive film to be obtained herein will be high and the heat resistance thereof will be low. If the atomic ratio of zinc oxide is smaller than 0.05, the transparent electroconductive film could not be etched satisfactorily. In this case, a small amount of water or hydrogen may be added to the system where the sintered product is sputtered to form films, whereby the etchability of the films formed could be improved. If the atomic ratio of zinc oxide is larger than 0.20, the electroconductivity of the transparent electroconductive film will be low. If the atomic ratio of tin oxide is smaller than 0.02, the electroconductivity of targets of the sintered product will be low; but if larger than 0.20, the surface resistance of the transparent electroconductive film formed will be high.
The sintered product comprises the basic constituent component, indium oxide alone, or indium oxide and zinc oxide and/or tin oxide, and contains from 0.5 to 10 atomic %, relative to the total of all metal atoms therein, an additional metal oxide selected from ruthenium oxide, molybdenum oxide and vanadium oxide. If the additional metal oxide content is smaller than 0.5 atomic %, the work function of the transparent electroconductive film to be obtained herein could not be increased to a satisfactory level; but if larger than 10 atomic %, the transparency of the film will be low. More preferably, the additional metal oxide content falls between 1 and 7 atomic %, even more preferably between 1 and 5 atomic %, relative to the total of all metal atoms in the composition.
The transparent electroconductive film from the sintered product that comprises the basic components of indium oxide and others and contains at least one additional component of ruthenium oxide, molybdenum oxide and vanadium oxide could have an increased work function of, for example, at least 5.45 electron volts when the proportion of the additional components falls within the defined range. The work function of the transparent electroconductive film is nearly on the same level as the average ionization potential, 5.5 to 5.6 electron volts, of organic compounds for light-emitting substances or hole-transporting substances for organic electroluminescent devices. Accordingly, when the transparent electroconductive film is used as the anode in an organic electroluminescent device, the energy gap in hole injection from the anode to the hole transportation layer or to the light-emitting layer in the device could be reduced, and therefore the device could ensure increased hole injection efficiency. As a result, the driving voltage for the organic electroluminescent device could be lowered, heat generation that may be caused by the energy gap between the constituent layers could be retarded in the device, and the device could ensure long-term stable light emission.
For producing the sintered product of the invention, for example, employed is a method comprising blending powders of the starting metal oxides in a predetermined ratio, uniformly mixing and grinding the blend in a mixing and grinding machine, for example, in a wet ball or bead mill or ultrasonically, then granulating the resulting mixture, shaping the resulting granules into bodies of desired form by pressing, and finally baking them into sintered products. In this, the raw material powders are preferably mixed and ground as fine as possible, but, in general, they are mixed and ground to have a mean grain size of not larger than 1 xcexcm. In the baking step, the shaped bodies are baked generally at a temperature falling between 1,200 and 1,500xc2x0 C., but preferably between 1,250 and 1,480xc2x0 C., for a period of time generally falling between 10 and 72 hours, but preferably between 24 and 48 hours. In this, the heating rate may fall between 1 and 50xc2x0 C./min.
[III] Third Aspect of the Invention
The transparent electroconductive material of the invention is of a composition that comprises one or more metal oxides selected from indium oxide, zinc oxide and tin oxide and contains from 0.5 to 20 atomic %, relative to the total of all metal atoms therein, of one or more metal oxides selected from iridium oxide, rhenium oxide and palladium oxide.
The transparent electroconductive material with better electroconductivity is of a composition that comprises metal oxide(s) of indium oxide, zinc oxide and tin oxide in the following atomic ratios:
In/(In+Zn+Sn)=0.00 to 1.00,
Zn/(In+Zn+Sn)=0.00 to 0.25,
Sn/(In+Zn+Sn)=0.00 to 1.00,
and contains from 0.5 to 20 atomic %, relative to the total of all metal atoms therein, of one or more metal oxides selected from iridium oxide, rhenium oxide and palladium oxide.
More preferably, the transparent electroconductive material is of a composition that comprises metal oxides of indium oxide, zinc oxide and tin oxide in the following atomic ratios:
In/(In+Zn+Sn)=0.50 to 1.00,
Zn/(In+Zn+Sn)=0.05 to 0.25,
Sn/(In+Zn+Sn)=0.00 to 0.50,
and contains from 0.5 to 20 atomic %, relative to the total of all metal atoms therein, of one or more metal oxides selected from iridium oxide, rhenium oxide and palladium oxide.
The transparent electroconductive material with much better electroconductivity is of a composition that comprises metal oxides of indium oxide, zinc oxide and tin oxide in the following atomic ratios:
In/(In+Zn+Sn)=0.75 to 0.95,
Zn/(In+Zn+Sn)=0.05 to 0.20,
Sn/(In+Zn+Sn)=0.00 to 0.20,
and contains from 0.5 to 20 atomic %, relative to the total of all metal atoms therein, of one or more metal oxides selected from iridium oxide, rhenium oxide and palladium oxide.
Most preferably, the transparent electroconductive material is of a composition that comprises metal oxides of indium oxide, zinc oxide and tin oxide in the following atomic ratios:
In/(In+Zn+Sn)=0.85 to 0.95,
Zn/(In+Zn+Sn)=0.07 to 0.20,
Sn/(In+Zn+Sn)=0.00 to 0.15,
and contains from 0.5 to 20 atomic %, relative to the total of all metal atoms therein, of one or more metal oxides selected from iridium oxide, rhenium oxide and palladium oxide.
For the transparent electroconductive material of the invention, the composition of the basic constituent components, indium oxide, zinc oxide and tin oxide, or a mixture of these metal oxides may be indium oxide, zinc oxide or tin oxide each alone, or a mixture of indium oxide and zinc oxide, or a mixture of indium oxide and tin oxide, or a mixture of indium oxide, zinc oxide and tin oxide, as in the above.
Regarding the blend ratio of the constituent components, indium oxide is not always needed herein. However, in order that the material could be formed into transparent electroconductive films with low surface resistance, it is desirable the atomic ratio of indium oxide is at least 0.5. Zinc oxide is not always needed herein. However, in order that the material could be formed into transparent electroconductive films with improved etchability, a small amount of zinc oxide is added to the composition for the material. For this, for example, the atomic ratio of zinc oxide may be at least 0.05. If the etchability of the transparent electroconductive films formed from the material is poor, a small amount of water or hydrogen may be added to the system where the sintered product of the material is sputtered to form the films, whereby the etchability of the films formed could be improved. If the atomic ratio of zinc oxide is larger than 0.25, the durability of the transparent electroconductive films will be low. Tin oxide is not always needed herein, but is preferably present in the material of the invention in order that targets formed from the material are desired to have high electroconductivity. However, when the transparent electroconductive films to be formed from the targets are desired to have low surface resistance, it is preferable that the atomic ratio of tin oxide is at most 0.5 in the material.
In the material, the basic constituent components shall be combined with any one of iridium oxide, rhenium oxide and palladium oxide or with a mixture of the metal oxides that may be in any desired ratio. The proportion of the additional metal oxides to be in the material shall fall between 0.5 and 20 atomic % relative to the total of all metal atoms constituting the material that includes the additional metal oxides. It may be given by the following formulae, in terms of the atomic ratio of the metals:
Ir/(In+Zn+Sn+Ir)=0.005 to 0.20,
Re/(In+Zn+Sn+Re)=0.005 to 0.20,
Pd/(In+Zn+Sn+Pd)=0.005 to 0.20,
preferably,
Ir/(In+Zn+Sn+Ir)=0.01 to 0.10,
Re/(In+Zn+Sn+Re)=0.01 to 0.10,
Pd/(In+Zn+Sn+Pd)=0.01 to 0.10,
more preferably,
Ir/(In+Zn+Sn+Ir)=0.03 to 0.08,
Re/(In+Zn+Sn+Re)=0.03 to 0.08,
Pd/(In+Zn+Sn+Pd)=0.03 to 0.08.
If the proportion of the additional components of iridium oxide, rhenium oxide and palladium oxide is smaller than 0.5 atomic %, the work function of the transparent electroconductive film to be obtained herein could not be increased to a satisfactory level; but if larger than 20 atomic %, the transparency of the film will be low.
The metal oxide composition comprising the basic constituent components as above and containing from 0.5 to 20 atomic %, relative to the total of all metal atoms therein, of iridium oxide, rhenium oxide and palladium oxide may be sintered to give sputtering targets, and the targets give transparent electroconductive films through sputtering. The films could have a light transmittance of at least 70%, and a work function of at least 5.4 electron volts. The work function of the films is nearly on the same level as the average ionization potential, 5.5 to 5.6 electron volts, of organic compounds for light-emitting substances or hole-transporting substances for organic electroluminescent devices. Accordingly, when the transparent electroconductive film is used as the anode in an organic electroluminescent device, the energy gap in hole injection from the anode to the hole transportation layer or to the light-emitting layer in the device could be reduced, and therefore the device could ensure increased hole injection efficiency. As a result, the driving voltage for the organic electroluminescent device could be lowered, heat generation that may be caused by the energy gap between the constituent layers could be retarded in the device, and the device could ensure long-term stable light emission.
For producing the transparent electroconductive material of the invention, for example, employed is a method comprising blending powders of the starting metal oxides in a predetermined ratio, followed by uniformly mixing and grinding the resulting blend in a mixing and grinding machine, for example, in a wet ball or bead mill or ultrasonically. In this, the raw material powders are preferably mixed and ground as fine as possible, but, in general, they are mixed and ground to have a mean grain size of not larger than 1 xcexcm.
To obtain sintered products from the transparent electroconductive material, for example, the material is granulated, then the resulting granules are shaped into bodies of desired form by pressing, and the shaped bodies are finally baked. In the baking step, the shaped bodies are baked generally at a temperature falling between 1,200 and 1,500xc2x0 C., but preferably between 1,250 and 1,480xc2x0 C., for a period of time generally falling between 10 and 72 hours, but preferably between 24 and 48 hours. In this, the heating rate may fall between 1 and 50xc2x0 C./min.
[IV] Fourth Aspect of the Invention
The transparent electroconductive material of the invention is of a composition that comprises metal oxide(s) of tin oxide, indium oxide and zinc oxide in the following atomic ratios:
Sn/(Sn+In+Zn)=0.55 to 1.00,
In/(Sn+In+Zn)=0.00 to 0.45,
Zn/(Sn+In+Zn)=0.00 to 0.25,
and contains from 0.5 to 10 atomic %, relative to the total of all metal atoms therein, of one or more metal oxides selected from vanadium oxide, molybdenum oxide and ruthenium oxide.
More preferably, the transparent electroconductive material is of a composition that comprises metal oxides of tin oxide, indium oxide and zinc oxide in the following atomic ratios:
Sn/(Sn+In+Zn)=0.60 to 0.95,
In/(Sn+In+Zn)=0.00 to 0.35,
Zn/(Sn+In+Zn)=0.05 to 0.20,
and contains from 0.5 to 10 atomic %, relative to the total of all metal atoms therein, of one or more metal oxides selected from vanadium oxide, molybdenum oxide and ruthenium oxide.
Even more preferably, the transparent electroconductive material is of a composition that comprises metal oxides of tin oxide, indium oxide and zinc oxide in the following atomic ratios:
Sn/(Sn+In+Zn)=0.55 to 0.95,
In/(Sn+In+Zn)=0.00 to 0.40,
Zn/(Sn+In+Zn)=0.05 to 0.25,
and contains from 0.5 to 10 atomic %, relative to the total of all metal atoms therein, of one or more metal oxides selected from vanadium oxide, molybdenum oxide and ruthenium oxide.
Still more preferably, the transparent electroconductive material is of a composition that comprises metal oxides of tin oxide, indium oxide and zinc oxide in the following atomic ratios:
Sn/(Sn+In+Zn)=0.55 to 0.95,
In/(Sn+In+Zn)=0.00 to 0.40,
Zn/(Sn+In+Zn)=0.05 to 0.20,
and contains from 0.5 to 10 atomic %, relative to the total of all metal atoms therein, of one or more metal oxides selected from vanadium oxide, molybdenum oxide and ruthenium oxide.
Most preferably, the transparent electroconductive material is of a composition that comprises metal oxides of tin oxide, indium oxide and zinc oxide in the following atomic ratios:
Sn/(Sn+In+Zn)=0.60 to 0.95,
In/(Sn+In+Zn)=0.00 to 0.35,
Zn/(Sn+In+Zn)=0.05 to 0.20,
and contains from 0.5 to 10 atomic %, relative to the total of all metal atoms therein, of one or more metal oxides selected from vanadium oxide, molybdenum oxide and ruthenium oxide.
For the transparent electroconductive material of the invention, the composition of the basic constituent components, tin oxide, indium oxide and zinc oxide, or a mixture of these metal oxides may be tin oxide, indium oxide or zinc oxide each alone, or a mixture of tin oxide and indium oxide, or a mixture of tin oxide and zinc oxide, or a mixture of tin oxide, indium oxide and zinc oxide, as in the above.
Regarding the blend ratio of the basic constituent components, it is desirable that the atomic ratio of tin oxide is at least 0.55 in order that the cost of the material could be reduced and that the material could be formed into transparent electroconductive films with good heat resistance. Indium oxide is not always needed herein. However, in order that the material could be formed into transparent electroconductive films with high electroconductivity, it is desirable the atomic ratio of indium oxide is at most 0.45. If the atomic ratio of indium oxide is larger than 0.45, the costs for producing transparent electroconductive films from the material will increase. Zinc oxide is not always needed herein. However, in order that the material could be formed into transparent electroconductive films with improved etchability, zinc oxide may be added to the composition for the material. The atomic ratio of zinc oxide to be added to the composition is preferably at least 0.05. In order to improve the wet heat resistance of the transparent electroconductive films formed from the material, the atomic ratio of zinc oxide to be in the material is preferably at most 0.25. If the etchability of the transparent electroconductive films formed from the material is poor, a small amount of water or hydrogen may be added to the system where the sintered product of the material is sputtered to form the films, whereby the etchability of the films formed could be improved.
In the material, the basic constituent components shall be combined with any one of vanadium oxide, molybdenum oxide and ruthenium oxide or with a mixture of the metal oxides that may be in any desired ratio. The proportion of the additional metal oxides to be in the material shall fall between 0.5 and 10 atomic % relative to the total of all metal atoms constituting the material that includes the additional metal oxides. It may be given by the following formulae, in terms of the atomic ratio of the metals:
V/(In+Zn+Sn+V)=0.005 to 0.10,
Mo/(In+Zn+Sn+Mo)=0.005 to 0.10,
Ru/(In+Zn+Sn+Ru)=0.005 to 0.10,
preferably,
V/(In+Zn+Sn+V)=0.01 to 0.08,
Mo/(In+Zn+Sn+Mo)=0.01 to 0.08,
Ru/(In+Zn+Sn+Ru)=0.01 to 0.08,
more preferably,
V/(In+Zn+Sn+V)=0.02 to 0.05,
Mo/(In+Zn+Sn+Mo)=0.02 to 0.05,
Ru/(In+Zn+Sn+Ru)=0.02 to 0.05.
If the proportion of the additional component of any of vanadium oxide, molybdenum oxide or ruthenium oxide or their mixture is smaller than 0.5 atomic %, the work function of the transparent electroconductive film to be obtained herein could not be increased to a satisfactory level; but if larger than 10 atomic %, the transparency of the film will be low.
The metal oxide composition comprising the basic constituent components as above and containing from 0.5 to 10 atomic %, relative to the total of all metal atoms therein, of vanadium oxide, molybdenum oxide or ruthenium oxide may be sintered to give sputtering targets, and the targets give transparent electroconductive films through sputtering. The films could have a light transmittance of at least 70%, and a work function of at least 5.4 electron volts. The work function of the films is nearly on the same level as the average ionization potential, 5.5 to 5.6 electron volts, of organic compounds for light-emitting substances or hole-transporting substances for organic electroluminescent devices. Accordingly, when the transparent electroconductive film is used as the anode in an organic electroluminescent device, the energy gap in hole injection from the anode to the hole transportation layer or to the light-emitting layer in the device could be reduced, and therefore the device could ensure increased hole injection efficiency. As a result, the driving voltage for the organic electroluminescent device could be lowered, heat generation that may be caused by the energy gap between the constituent layers could be retarded in the device, and the device could ensure long-term stable light emission.
For producing the transparent electroconductive material of the invention, for example, employed is a method comprising blending powders of the starting metal oxides in a predetermined ratio, followed by uniformly mixing and grinding the resulting blend in a mixing and grinding machine, for example, in a wet ball or bead mill or ultrasonically. In this, the raw material powders are preferably mixed and ground as fine as possible, but, in general, they are mixed and ground to have a mean grain size of not larger than 1 xcexcm.
To obtain sintered products from the transparent electroconductive material, for example, the material is granulated, then the resulting granules are shaped into bodies of desired form by pressing, and the shaped bodies are finally baked. In the baking step, the shaped bodies are baked generally at a temperature falling between 1,200 and 1,500xc2x0 C., but preferably between 1,250 and 1,480xc2x0 C., for a period of time generally falling between 10 and 72 hours, but preferably between 24 and 48 hours. In this, the heating rate may fall between 1 and 50xc2x0 C./min. The sintered products formed under the condition could have a specific resistance of at most 10 mxcexa9.cm.
The sintered products thus obtained are machined into bodies fittable to sputtering units, and a fitting tool is attached to each body. In that manner, obtained are sputtering targets with good electroconductivity that could be sputtered stably.
[V] Transparent Electroconductive Glass and Films of the First to Fourth Aspects of the Invention
The targets produced in the manner mentioned above may be sputtered to form films on transparent substrates. The transparent substrates may be any conventional one, including glass substrates, and synthetic resin films and sheets with high transparency. Preferred synthetic resins for the films and sheets are polycarbonate resins, polymethyl methacrylate resins, polyester resins, polyether-sulfone resins, polyarylate resins, etc.
For sputtering the targets to form transparent electroconductive films on transparent substrates, preferably used are magnetron sputtering units. The sputtering condition in the unit where the films are formed is described. The plasma output may vary, depending on the surface area of the target used and on the thickness of the transparent electroconductive film to be formed, but, in general, it may fall between 0.3 and 4 W per cm2 of the surface area of the target, and the period of time for which the target is sputtered to form the film may fall between 5 and 120 minutes. Under the condition, the transparent electroconductive films formed could have a desired thickness. The thickness of the transparent electroconductive films shall vary, depending on the type the display devices in which they are sued, but, in general, it may fall between 200 and 6000 angstroms, preferably between 300 and 2000 angstroms.
The targets of the sintered products may also be used for forming films in electron-beaming units or ion-plating units. In these units, the targets could be formed into transparent electroconductive films under the same condition as above.
In the transparent electroconductive glass and films of the invention thus produced in the manner as above, the transparent electroconductive layer formed on a transparent substrate has high light transmittance and low specific resistance. The transparent electroconductive layer is well etched to give a transparent electrode. Specifically, after it is etched with hydrochloric acid or oxalic acid, its cross section in the boundary between the etched part and the non-etched part has a smooth profile, and the etched part is clearly differentiated from the non-etched part. The etched layer forms an electrode line circuit having a uniform width and a uniform thickness. Accordingly, the transparent electroconductive layer in the transparent electroconductive glass and films of the invention can be well etched in any ordinary manner to give good transparent electrodes. When a transparent electroconductive film with poor processability into electrodes is etched to form an electrode, the electric resistance of the circuit that comprises the resulting electrode will partly increase or decrease, and, as the case may be, the insulating area in the circuit will fail to prevent electric conduction and the circuit will break down. Contrary to this, the circuit that comprises the transparent electrode fabricated in the invention is free from the troubles.
In the first aspect of the invention, the transparent electroconductive layer formed from the sintered product that comprises the three-component metal oxides and containing an oxide of a positive tetra-valent or higher poly-valent metal has a high light transmittance of at least 75% and are therefore highly transparent. In addition, It has a specific resistance of at most 5 mxcexa9.cm and a work function of at least 5.45. With the layer, the transparent electroconductive glass and films of the invention are favorable to transparent electrodes for organic electroluminescent devices. In this embodiment, if the proportion of the additional metal oxide with a positive tetra-valent or higher poly-valent metal is too large, the electroconductivity of the layer will be low. Therefore, when the layer is desired to have high electroconductivity, it shall have a laminate structure comprising a lower layer of the three-component metal oxides and an upper layer of the additional metal oxide with a positive tetra-valent or higher poly-valent metal. Thus layered, the two shall be sintered. The two-layered, transparent electroconductive layer could have higher electroconductivity, and its work function could be nearly on the same level as that of organic compounds for organic electroluminescent devices. The layer is favorably used as an electrode in organic electroluminescent devices.
In the transparent electroconductive glass and films of the second aspect of the invention thus produced in the manner as above, the metal oxide composition of the transparent electroconductive layer is the same as that of the sintered product used for forming the layer. Regarding its transparency, the transparent electroconductive layer has a light transmittance of larger than 75% for light having a wavelength of 500 nm. Regarding its electroconductivity, the layer has a specific resistance of at most 5 mxcexa9.cm. As mentioned hereinabove, the work function of the layer is at least 5.45 electron volts and is higher than that of ordinary ITO films.
In the transparent electroconductive glass and films of the third aspect of the invention thus produced in the manner as above, the metal oxide composition of the transparent electroconductive layer is the same as that of the sintered product used for forming the layer. Regarding its transparency, the transparent electroconductive layer has a light transmittance of larger than 70% for light having a wavelength of 500 nm. Regarding its electroconductivity, the layer generally has a specific resistance of at most 5 mxcexa9.cm. As mentioned hereinabove, the work function of the layer is higher than that of ordinary ITO films, and is at least 5.4 electron volts nearly on the same level as the ionization potential of organic compounds for light-emitting layers or hole transportation layers in organic electroluminescent devices.
In the transparent electroconductive glass and films of the fourth aspect of the invention thus produced in the manner as above, the metal oxide composition of the transparent electroconductive layer is the same as that of the sintered product used for forming the layer. Regarding its transparency, the transparent electroconductive layer has a light transmittance of larger than 70% for light having a wavelength of 500 nm. As mentioned hereinabove, the work function of the layer is higher than that of ordinary ITO films, and is at least 5.4 electron volts nearly on the same level as the ionization potential of organic compounds for light-emitting layers or hole transportation layers in organic electroluminescent devices.
Accordingly, the transparent electroconductive glass and films of the invention are favorably used as transparent electrodes in various display devices such as typically organic electroluminescent devices.
The invention is described in more detail with reference to the following Examples, which, however, are not intended to restrict the scope of the invention.
First Aspect of the Invention